For certain applications, such as for windscreens or wing mirrors for motor vehicles, it would be desirable to provide a transparent heating device in the form of a transparent element that is capable of conducting an electrical current across its surface. Thus, by applying a voltage to electrodes at the edges of the transparent element, the transparent element may be heated. In the case of windscreens or wing mirrors, such a heating device can be used to remove and/or prevent the build-up of frost.
Indium tin oxide (ITO) is a material that, when applied in thin layers, provides a transparent conducting layer. However, ITO has a number of drawbacks. In particular, it is a relatively brittle material, making it unsuitable for surfaces that may flex during use. Furthermore, Indium is in short supply, making ITO relatively costly.
One alternative to ITO that has been proposed is graphene. Graphene is a material composed of carbon atoms forming a crystal lattice one atom in thickness. It is conductive, transparent, and flexible and can be produced at relatively low cost. For example, the publication by J. Kang et al. entitled “High-Performance Graphene-Based Transparent Flexible Heaters”, Nano Letters, 3b2, version 9, pages 5154 to 5158, Nov. 14, 2011, describes a flexible transparent heater based on a large-scale graphene film synthesized by chemical vapor deposition on a Cu foil.
However, there is a technical problem in providing a transparent heating device comprising graphene that has a relatively uniform thermal emission across its surface.
Furthermore would also be desirable in some embodiments to be able to display information on the transparent heating device, however there are technical problems in doing so.